More than Encoder: Introducing Transformer Decoder to Upsample
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General segmentation models downsample images and then upsample to restore resolution for pixel level prediction. In such schema, upsample technique is vital in maintaining information for better performance. In this paper, we present a new upsample approach, Attention Upsample (AU), that could serve as general upsample method and be incorporated into any segmentation model that possesses lateral connections. AU leverages pixel-level attention to model long range dependency and global information for better reconstruction. It consists of Attention Decoder (AD) and bilinear upsample as residual connection to complement the upsampled features. AD adopts the idea of decoder from transformer which upsamples features conditioned on local and detailed information from contracting path. Moreover, considering the extensive memory and computation cost of pixel-level attention, we further propose to use window attention scheme to restrict attention computation in local windows instead of global range. Incorporating window attention, we denote our decoder as Window Attention Decoder (WAD) and our upsample method as Window Attention Upsample (WAU). We test our method on classic U-Net structure with lateral connection to deliver information from contracting path and achieve state-of-the-arts performance on Synapse (80.30 DSC and 23.12 HD) and MSD Brain (74.75 DSC) datasets.
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